Patch "perf: Copy perf_event_attr::sig_data on modification" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    perf: Copy perf_event_attr::sig_data on modification

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     perf-copy-perf_event_attr-sig_data-on-modification.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7f91eff84f27e598f934292adebb451aa15d1552
Author: Marco Elver <elver@xxxxxxxxxx>
Date:   Mon Jan 31 11:34:05 2022 +0100

    perf: Copy perf_event_attr::sig_data on modification
    
    [ Upstream commit 3c25fc97f5590060464cabfa25710970ecddbc96 ]
    
    The intent has always been that perf_event_attr::sig_data should also be
    modifiable along with PERF_EVENT_IOC_MODIFY_ATTRIBUTES, because it is
    observable by user space if SIGTRAP on events is requested.
    
    Currently only PERF_TYPE_BREAKPOINT is modifiable, and explicitly copies
    relevant breakpoint-related attributes in hw_breakpoint_copy_attr().
    This misses copying perf_event_attr::sig_data.
    
    Since sig_data is not specific to PERF_TYPE_BREAKPOINT, introduce a
    helper to copy generic event-type-independent attributes on
    modification.
    
    Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events")
    Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
    Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220131103407.1971678-1-elver@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index c7581e3fb8ab1..69c70767b5dff 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3234,6 +3234,15 @@ static int perf_event_modify_breakpoint(struct perf_event *bp,
 	return err;
 }
 
+/*
+ * Copy event-type-independent attributes that may be modified.
+ */
+static void perf_event_modify_copy_attr(struct perf_event_attr *to,
+					const struct perf_event_attr *from)
+{
+	to->sig_data = from->sig_data;
+}
+
 static int perf_event_modify_attr(struct perf_event *event,
 				  struct perf_event_attr *attr)
 {
@@ -3256,10 +3265,17 @@ static int perf_event_modify_attr(struct perf_event *event,
 	WARN_ON_ONCE(event->ctx->parent_ctx);
 
 	mutex_lock(&event->child_mutex);
+	/*
+	 * Event-type-independent attributes must be copied before event-type
+	 * modification, which will validate that final attributes match the
+	 * source attributes after all relevant attributes have been copied.
+	 */
+	perf_event_modify_copy_attr(&event->attr, attr);
 	err = func(event, attr);
 	if (err)
 		goto out;
 	list_for_each_entry(child, &event->child_list, child_list) {
+		perf_event_modify_copy_attr(&child->attr, attr);
 		err = func(child, attr);
 		if (err)
 			goto out;